Crude oil produced from an oil well usually is pumped into a large storage tank holding hundreds of barrels of oil, and then the crude is continuously pumped from the storage tank and metered into a sales line. A small sample of the crude is removed from the flow line located downstream of the storage tank and the sample subsequently is used to determine the quality of the crude. This removed sample determines the price to be paid for the crude. The exact amount of money received for the crude oil is determined by gravity, sediment and water content. For example, fifteen cents per barrel is deducted for each one degree API increment below four degrees API for sour crude. Therefore, 0.4.degree. API gravity increase would increase the price of the oil transferred to sales by six cents per barrel. This represents a lot of money when it comes to crude oil sales.
Oil stored in a vessel loses quality because the light ends cook off or escape into the atmosphere, also called weathering. Moreover, there is dirt, water, and other materials that gravitate toward the bottom of the storage tank that must be accounted for. Heretofore, it has not been possible to obtain a true representative sample of the hydrocarbons from crude that has accumulated in a sample vessel for many days.
Accordingly, it would be desirable to sequentially eject a finite quantity of produced crude flowing from a storage tank. These increments of oil accumulate concurrently with the flow of the crude from the storage tank, and therefore, the crude contained within the sample vessel is protected and is truly representative of the flow from the storage tank.
The method presently used to try to obtain a representative production sample is carried out on the contents of a small sample container. The gauger circulates the entire sample in the pot in order to place as much of the water and sludge contained in the bottom of the storage pot into suspension as is possible. The first substance to go through the circulation pump is water which is circulated back on top of the sample. The industry recommends that this circulation procedure continue for fifteen minutes, which is not always adhered to. Next, a 50cc sample is obtained downstream of the pump, and the sample is heated and then centrifuged to obtain the percent composition of the water and sediments. A reduction of the months volume of sales is based on this crude test.
Next, approximately one quart sample is removed from the pot which is subjected to an API gravity test. This sample is allowed to stand until all of the foam has broken out of the sample. The foamy action is caused by a sudden reduction of pressure which causes the hydrocarbon gases or light ends to escape into the atmosphere. These gases that escape into the atmosphere are light ends of hydrocarbons which have definite values in their relationship to the gravity of the oil.
These tests are carried out in order to arrive at the value of each months sales of the crude. It is apparent that these tests are inaccurate. The present invention insures that a true representative sample of the total months production is analyzed and that accurate gravity and S & W content can be ascertained.
S & W, as used herein, means sediment and water and once upon a time was called "BS & W".